on the heater thing, 1 side of the transformer is connected to pins 4 and 5 on the 12AX7 and the other side is attatched to pin 9. and about the 12AX7's on 150v, ive just found 12AX7s on lower voltage than 200v either dont have alot of headroom for clean sounds, and just dont sound as good as they can.
Exactly. R2 & R3 100R, R1 around 220K, R4 around 47K. You can also throw a series R on each 6.3V leg if you need to drop a little voltage to the filament.
awesome. thanks guys! I cant wait to get eh parts and start playing! i really need ot find a good trafo for the plexi though...i think im going to try emailing edcor with the specs i need and see if they have one already (i would rather not pay the $40 setup fee if i can avoid it) you guys think 300+ is good for the plexi design?
Can you post a screenshot of your PSUD schemo? Don't worry about getting the messages. Are you modeling the Champ PS? Have you changed the load R to constant current?
I use current taps for all the stages, as I have no idea what the equivalent R would be. If you have a schematic of the power supply, post that also.
sweet got it working! jsut out of curiosity, how much resistance do you set your caps and inductors to? i figure the caps should be high and the inductors should be low, but i dont really know how much they are in real life. also, does anyone know the value/specs of the choke used in the 5E1 schematic?does 2mA for the 12AX7 stages combined and 30mA for the SE 6v6 sound right to you guys?
I leave the DCR of the caps at the default value, which IIRC is 2 ohms. For Chokes, do a search for Hammond 159 series, and use the resistance values in the Hammond table for whatever L value you are modeling, that'll be close to reality. Modeling the secondary R of the power transformer is a little tougher if you don't have it in hand.
Are you going to post a screen shot of your PSUD model?
Are you going to post a screen shot of your PSUD model?
Im not sure if you can run these, but i couldnt get a good screen shot of the models on this computer for some reason. if you cant open them for some reason, let me know. i cant try to get better screen shots on my desktop. the champ one works (although the 12AX7 voltages are a little low) and the plexi seems to have errors, so im working on trying to fix that
I got the files to unzip no problem
The functional zip file is better than a screen shot, since I don't have to build the model! That's cool. When the PSUD is ironed out, a posted screen shot may help others.
I'll play with these later today (I've gotta buy some lumber this am for my patio cover project).
Looks good so far.... Any reason that you used EZ81 rectifier instead of 5Y3?
The functional zip file is better than a screen shot, since I don't have to build the model! That's cool. When the PSUD is ironed out, a posted screen shot may help others.
I'll play with these later today (I've gotta buy some lumber this am for my patio cover project).
Looks good so far.... Any reason that you used EZ81 rectifier instead of 5Y3?
I tried both, to see the differences, i just tried the EZ81 after the 5Y3. I am trying to decide which to go with (as the price difference on the trafos is pulling me towards a 6.3v heater) and someone mentioned the EZ81 as a good 6.3v rectifier. I am tempted to go with the 5Y3 simply because it was what is used in the amp though.
Lynchy: Your champ PSUD model looks fine. I've only built hi-fi tube stuff so I don't know if larger caps in the power supply are a good or bad thing for a MI amp. The 8uf and 16uf stuff shown on the orig schematic were what was available for cheap back in the day. Those small values result in a lot of ripple voltage which will show up as hum on the output. Use the magnifier buttons in the upper right corner of PSUD to first zoom out, then zoom in very tight a couple of times on the higher voltage. You've got about 300mv of ripple. Increasing the cap values (esp. C2) will bring this way down. Model it with C2=100uf and C2=220uf and see what happens.
With a tube rectifier, the value of C1 has to remain quite low (look at the datasheets for EZ81 & 5Y3) or the tube will arc over on start-up, due to the inrush current that an empty first cap needs to charge. Tube rectifiers also depend on high output impedance from the transformer to prevent arc over. Reduce the 50 ohm transformer resistance down to 1 ohm (leave C2 at 220uf) and see what happens. There is a max value of C1 for a given current draw for tube rectifiers as well as minimum output impedance of the power transformer.
Also for fun, reduce the value of C1 from 8uf down to say 4, 2, 1, .1uf and see what happens to B+.......an easy way to reduce volts without burning lots of power in a big honkin resistor.
Again, I'm no expert here but I think you want a relatively high output impedance PS with some decent sized caps, that will give you minimal mains hum at the output with some voltage sag when overdriven. This may be obvious, but power transformers with lower current ratings have higher secondary winding resistance than higher current models, so resist the urge to overspec the power transformer current rating.
When designing tube Hi-fi power amps, we usually want a low PS output impedance, which is typically a transformer spec'd with a little higher than the needed current draw, SS diode rectification, and 100u-300u caps. This gives a stiff, quiet supply, ie low output impedance/no voltage sag.
One comment on the plexi PSUD model: You have a SS bridge rectifier modeled, try it also with a SS FWCT. Either way works, although most tube power transformers are center tapped.
With a tube rectifier, the value of C1 has to remain quite low (look at the datasheets for EZ81 & 5Y3) or the tube will arc over on start-up, due to the inrush current that an empty first cap needs to charge. Tube rectifiers also depend on high output impedance from the transformer to prevent arc over. Reduce the 50 ohm transformer resistance down to 1 ohm (leave C2 at 220uf) and see what happens. There is a max value of C1 for a given current draw for tube rectifiers as well as minimum output impedance of the power transformer.
Also for fun, reduce the value of C1 from 8uf down to say 4, 2, 1, .1uf and see what happens to B+.......an easy way to reduce volts without burning lots of power in a big honkin resistor.
Again, I'm no expert here but I think you want a relatively high output impedance PS with some decent sized caps, that will give you minimal mains hum at the output with some voltage sag when overdriven. This may be obvious, but power transformers with lower current ratings have higher secondary winding resistance than higher current models, so resist the urge to overspec the power transformer current rating.
When designing tube Hi-fi power amps, we usually want a low PS output impedance, which is typically a transformer spec'd with a little higher than the needed current draw, SS diode rectification, and 100u-300u caps. This gives a stiff, quiet supply, ie low output impedance/no voltage sag.
One comment on the plexi PSUD model: You have a SS bridge rectifier modeled, try it also with a SS FWCT. Either way works, although most tube power transformers are center tapped.
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I feel like a lot of this stuff im going to have to jsut play around with different values once i get a working prototype. Thank you guys so much for helping me out with this. I feel like ive learned a lot so far and i havent even gotten the parts yet! i cant wait. the only thing left to order is a power trafo for the plexi. i found one thats a little smaller then i want voltage-wise, so i may use a doubler to get it where i want it.
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in that case, i think ive found my trafo:
EDCOR Electronics Corporation. XPWR105-120
for some reason when i did the math earlier, i counted 300mA for each stage, rather than each tube, which made me think i needed an extra 900mA in the 6.3v winding. the voltage is pretty high on this one, but the EH 6v6's are rated at 450v, so if i can't get it down as low it still shouldnt fry my tubes. between that and a low value on the first cap in a CLC supply, I should be able to make it work. as long as i can keep the plate dissipation to 14W or less
EDCOR Electronics Corporation. XPWR105-120
for some reason when i did the math earlier, i counted 300mA for each stage, rather than each tube, which made me think i needed an extra 900mA in the 6.3v winding. the voltage is pretty high on this one, but the EH 6v6's are rated at 450v, so if i can't get it down as low it still shouldnt fry my tubes. between that and a low value on the first cap in a CLC supply, I should be able to make it work. as long as i can keep the plate dissipation to 14W or less
Lynchy: That transformer secondary voltage is too low, and the current rating is way too high. Model that as a FWCT 180-0-180 and you'll see what I mean, you're going to end up with less than 1.41*180V for a max B+.
The classic champ circuit calls for a 650V CT (325-0-325) at 70 ma. Triode electronics has some interesting power transformers and transformer kits for champ clones.
Here's another site calling for a 250-0-250 power transformer, perhaps a slightly different champ circuit.
http://www.ampbooks.com/home/classic-circuits/fender-champ-5e1-power-supply/
In Edcor's offerings, look for something along the lines of the XPWR014-120. The XPWR123 also looks good, but unfortunately only avail in 100V mains.
For the Plexi, the XPWR015-120 looks interesting but it would nice if it had a bias tap......
The classic champ circuit calls for a 650V CT (325-0-325) at 70 ma. Triode electronics has some interesting power transformers and transformer kits for champ clones.
Here's another site calling for a 250-0-250 power transformer, perhaps a slightly different champ circuit.
http://www.ampbooks.com/home/classic-circuits/fender-champ-5e1-power-supply/
In Edcor's offerings, look for something along the lines of the XPWR014-120. The XPWR123 also looks good, but unfortunately only avail in 100V mains.
For the Plexi, the XPWR015-120 looks interesting but it would nice if it had a bias tap......
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